Phase change memory in a dual inline memory module

ABSTRACT

Subject matter disclosed herein relates to management of a memory device.

BACKGROUND

1. Field

Subject matter disclosed herein relates to management of a memory device.

2. Information

Memory devices are employed in many types of electronic devices, such as computers, cell phones, PDA's, data loggers, games, and navigational equipment, for example. Among such electronic devices, various types of memory devices may be employed, such as NAND and NOR flash, SRAM, DRAM, and phase-change, just to name a few examples. Corresponding to increases in operating speed and cache line sizes, memory devices may be packaged in a dual inline memory module (DIMM) configuration. For example, such a DIMM, which may be used as a main memory in a computing platform, may comprise a number of DRAM memory modules mounted in parallel on the DIMM. Accordingly, a read/write request to the DIMM may be split across parallel DRAM modules so that individual DRAM modules provide a subset of total cache line request. Such DRAM devices typically have particular intrinsic parameters associated with read/write timing, memory page size, and/or addressing protocol, just to name a few examples.

BRIEF DESCRIPTION OF THE FIGURES

Non-limiting and non-exhaustive embodiments will be described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various figures unless otherwise specified.

FIG. 1 is a schematic diagram of a memory configuration, according to an embodiment.

FIG. 2 is a schematic diagram of a memory configuration, according to another embodiment.

FIG. 3 is a timing diagram of a memory control process, according to an embodiment.

FIG. 4 is a flow diagram of a memory control process, according to an embodiment.

FIG. 5 is a schematic view of a computing system and a memory device, according to an embodiment.

DETAILED DESCRIPTION

Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of claimed subject matter. Thus, the appearances of the phrase “in one embodiment” or “an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in one or more embodiments.

In an embodiment, a memory device may comprise a dual inline memory module (DIMM) that includes phase change memory (PCM) modules. Such PCM modules may be mounted and electronically connected in parallel on a DIMM. In one implementation, such a DIMM, which may comprise at least a portion of a main memory of a computing system for example, may include a memory bus to communicate with a memory controller. Through such a memory bus, a computing system may access PCM modules on a DIMM via a memory controller.

In one embodiment, a DIMM may be adapted to electronically operate based, at least in part, on dynamic random access memory (DRAM) modules. For example, a DIMM may comprise one or more DRAM sockets to receive one or more PCM modules, though claimed subject matter is not so limited. For another example, one or more PCM modules may comprise DRAM mode registers and/or a DRAM interface including connections adapted for a DRAM. PCM modules may be incorporated in such a DIMM by using appropriate memory-level and/or system-level processes and/or parameters, as explained in greater detail below. For example, a computing system may comprise a basic input/output system (BIOS) that maintains parameters corresponding to PCM modules. Such parameters may, for example, comprise values for timing, latencies, and/or size of PCM modules. In a particular implementation, a BIOS need not test PCM modules upon a system boot. Such a BIOS may include a low-level driver configured to operate PCM modules. In addition, such a BIOS may include executable code to read PCM module identification (ID) and to be responsive to PCM module configuration. For another example, PCM modules may be associated with an additive latency that enables a column address, generated by a memory controller for example, to be provided to a DIMM immediately after the DIMM receives a row address. Such additive latency may be introduced in a timing scheme of PCM modules so that consecutive read commands directed to the PCM may immediately follow one another without delay and without introducing timing gaps in output data, for example.

In general, writing or programming processes may be used to store information in memory devices, while a read process may be used to retrieve stored information. Stored information may be erased from all or a portion of a memory device and/or new information may be written into all or a portion of memory device. Relatively large numbers of such program-erase and/or program-re-program cycles may degrade the physical integrity of a PCM. For example, thousands of program-erase cycles imposed on a DIMM that incorporates PCM may reduce a reliability of the DIMM. If using such PCM memory, it may be beneficial to limit and/or reduce the number of occurrences of program-erase cycles, or “cycling”, that a PCM memory may otherwise be subjected to. Accordingly, in one embodiment, a technique to manage cycling of PCM modules on a DIMM may comprise caching write data. In particular, a memory device, such as a DRAM cache memory, may be used to cache write data corresponding to particular addresses of a PCM DIMM. A memory size of such a DRAM cache memory may be selected based, at least in part, on properties of PCM modules comprising a PCM DIMM. Such properties may include PCM DIMM size, for example. Such properties may include, for example, cycling specifications of PCM, PCM failure rate, PCM write speed, write usage model of a system incorporating a PCM DIMM, and/or PCM write wear leveling techniques used. As a particular example, a size of such a DRAM cache memory may range from about 100 KB to several tens of megabytes RAM, though claimed subject matter is not so limited.

In one implementation, a PCM DIMM may include PCM modules stacked in a package with multiple memory dice per package. For example, such a package may comprise two, four, or eight dice per package, providing one, two, four, or eight I/O pins, respectively. A result of such an implementation may be that additional PCM may be used without presenting extra loading on output drivers, for example. Also, if PCM used in a DIMM has a smaller number of banks (partitions) than that of a DRAM, bank address bits may be used to access multiple banks across multiple PCM devices, as explained in further detail below.

FIG. 1 is a schematic diagram of a DRAM DIMM 100 that comprises multiple DRAM modules, according to an embodiment, including DRAM 110, DRAM 120, and DRAM 130, which are shown in the figure. Although eight DRAM modules may be included in a particular embodiment, a DRAM DIMM may include any number of DRAM modules. For example, a ninth DRAM module may be present to provide error correction, though claimed subject matter is not so limited to such an example. Individual DRAM modules may comprise a matrix of addressable memory cells that are accessed by first specifying a row address after which a column address is specified. Block arrow 150 represents an address bus through which a memory controller (not shown) may provide a read/write address to DRAM DIMM 100. In one particular implementation, such an address bus may be sixteen bits wide. Block arrow 160 represents a data bus through which parallel data from/to DRAM modules may provide read data or receive write data to/from the memory controller and/or other portion of a computing system (not shown). In one particular implementation, such a data bus may be sixty-four bits wide to account for eight eight-bit DRAM modules connected in parallel, though claimed subject matter is not so limited. To address a particular location on DRAM DIMM 100, an activate command, explained in further detail below, may be accompanied by a row address provided to DRAM modules 110 through 130 by a memory controller, for example, on a bus represented by block arrows 140. Such a row address bus 140 may be connected in parallel to individual DRAM modules. Subsequent to providing a row address, a memory controller may generate a read/write command accompanied by a column address provided to the individual DRAM modules via a bus represented by block arrows 170. Of course, such features and details of a DRAM DIMM are merely examples, and claimed subject matter is not so limited.

FIG. 2 is a diagram view of a PCM DIMM 200 that comprises multiple PCM modules, according to an embodiment, including PCM 214, PCM 218, PCM 224, and PCM 228. PCM DIMM 200 may be adapted to electronically operate based, at least in part, on DRAM modules. In such a case, more than one PCM module may be used in place of one DRAM module, depending, at least in part, on the number of memory banks in individual PCM modules. Accordingly, PCM DIMM 200 may comprise a memory site 210 where PCM 214 and/or PCM 218 are used in place of one DRAM module and a memory site 220, where PCM 224 and/or PCM 228 may used in place of another DRAM module. Here, a memory site refers to a location of PCM DIMM 200 where electronic connections between PCM DIMM 200 and a DRAM or PCM modules may be made. In a particular implementation, a PCM module may involve more electronic connections than a DRAM module. For example, PCM DIMM 200 may include PCM modules that have four banks and three-bit bank addresses (capable of addressing up to eight banks); two PCM devices each with four bank addresses may then be accessed. Accordingly, in a particular implementation, a PCM DIMM may be provided with bank address bits that correspond to multiple memory banks across multiple PCM devices. Of course, such memory sites may include more or less than the number of PCM modules shown and described in the present example embodiment. Similarly, PCM DIMM 200 may include more or less than the number of such memory sites shown and described in the present example embodiment. Accordingly, claimed subject matter is not so limited to such details.

Similar to DRAM modules described above, individual PCM modules may comprise a matrix of addressable memory cells which are accessible by first specifying a row address after which a column address is specified. Block arrow 240 represents an address bus through which a memory controller (not shown) may provide a read/write address to PCM DIMM 200. In one particular implementation, such an address bus may be sixteen bits wide, for example. Block arrow 250 represents a data bus through which parallel data from/to PCM modules may provide read data or receive write data to/from the memory controller and/or other portion of a computing system (not shown). In one particular implementation, such a data bus may be sixty-four bits wide to account for eight parallel groups of PCM modules, each group having eight bits connected in parallel, though claimed subject matter is not so limited. To address a particular location on PCM DIMM 200, an activate command, explained in further detail below, may be accompanied by a row address provided to PCM modules 214 through 228 by a memory controller, for example, on a bus represented by block arrows 230. Such an address bus 230 may be connected in parallel to individual PCM modules. Subsequent to providing a row address, a memory controller may generate a read/write command accompanied by a column address provided to individual memory sites 210 through 220 via a bus 230. Such a column address accompanied by a read/write command may also be provided to individual PCM modules 214 though 228 via a bus represented by block arrows 260. Of course, such features and details of a PCM DIMM are merely examples, and claimed subject matter is not so limited.

FIG. 3 is a timing diagram of a memory control process 300, and FIG. 4 is a flow diagram of a memory control process 400, according to an embodiment. The following descriptive example is based on memory control process 300 and memory control process 400 comprising the same process, though claimed subject matter is not so limited. As shown in FIG. 3, a clock signal 305 may establish timing of memory processes. At block 410, a memory controller may issue an activate command 310 to open a page or memory bank of a PCM module, such as PCM module 214 shown in FIG. 2, for example. During such an activate phase, a PCM module may receive a row address 315 from a memory controller, as in block 420. At blocks 430 and 440, a memory controller may issue a read instruction 320 and a column address 325, thus providing a memory address (row and column) of one or more memory cells from where data is to be read. In a particular implementation, an additive latency may be used to improve memory process scheduling: a row address and a column address may be issued back-to-back, thereby avoiding timing gaps in output data, for example. Such timing gaps, however, may be desirable in some applications, and claimed subject matter is not so limited. For example, though not shown in FIG. 3, there may be one or more clock cycles between activate command 310 and read instruction 320. In detail, utilizing column address strobe (CAS) latency and/or additive latency, a read instruction may be issued immediately after an activate command. Such a read instruction need not be delayed internally by a predetermined number of clock cycles (hence additive latency) before being executed. Because such a timing process is performed without need for an additional command, collision among memory instructions may be avoided.

Though not needed for one or more embodiments described herein, a value for additive latency may be maintained in a mode register of the PCM module. Accordingly, at block 450, a period ICCD lapses before another read instruction 330 is issued, at block 460. Concurrently, another column address may be issued, as at block 470. After one or more latencies, such as read latency and column addressing latency for example, data 340 may result from read instruction 320 and data 350 may result from read instruction 330. In one implementation, a process of providing column addresses and reading memory at the corresponding addresses may repeat until, for example, a final column of the opened page is reached, as checked at block 480. In such a case, another activate command may be issued by a memory controller to open another page. As indicated above, PCM modules may be incorporated in a DIMM that is adapted to electronically operate based, at least in part, on DRAM modules. To accommodate such PCM modules, appropriate memory-level and/or system-level processes and/or parameters, may be implemented. For example, at a system level, a BIOS may retrieve parameters from one or more mode registers maintained in PCM modules or other memory. Such parameters, comprising values for read latency, write latency, CAS latency, internal read command to first data time, activate to internal read/write delay, and/or additive delay, just to name a few examples, may correspond to the PCM modules.

FIG. 5 is a schematic diagram illustrating an exemplary embodiment of a computing system 500 including a memory device 510. A computing device 504 may be representative of any device, appliance, or machine that may be configurable to manage memory device 510. Memory device 510 may include a memory controller 515 and a memory 522. By way of example but not limitation, computing device 504 may include: one or more computing devices and/or platforms, such as, e.g., a desktop computer, a laptop computer, a workstation, a server device, or the like; one or more personal computing or communication devices or appliances, such as, e.g., a personal digital assistant, mobile communication device, or the like; a computing system and/or associated service provider capability, such as, e.g., a database or data storage service provider/system; and/or any combination thereof.

It is recognized that all or part of the various devices shown in system 500, and the processes and methods as further described herein, may be implemented using or otherwise including hardware, firmware, software, or ally combination thereof. Thus, by way of example but not limitation, computing device 504 may include at least one processing unit 520 that is operatively coupled to memory 522 through a bus 540 and a host or memory controller 515. Processing unit 520 is representative of one or more circuits configurable to perform at least a portion of a data computing procedure or process. By way of example but not limitation, processing unit 520 may include one or more processors, controllers, microprocessors, microcontrollers, application specific integrated circuits, digital signal processors, programmable logic devices, field programmable gate arrays, and the like, or any combination thereof. Processing unit 520 may communicate with memory controller 515 to process memory-related operations, such as read, write, and/or erase, as well as memory partition processes discussed above, for example. Processing unit 520 may include an operating system adapted to communicate with memory controller 515. Such an operating system may, for example, generate commands to be sent to memory controller 515 over bus 540. Such commands may include read/write instructions, for example. Computing device 504 may comprise a basic input/output system (BIOS) that maintains parameters corresponding to PCM modules, which may be associated with an additive latency that enables a column address, generated by memory controller 515 for example, to be provided to a DIMM immediately after the DIMM receives a row address.

Memory 522 is representative of any data storage mechanism. Memory 522 may include, for example, a primary memory 524 and/or a secondary memory 526. In a particular embodiment, memory 522 may comprise a PCM DIMM, as described above. In particular, primary memory 524 may include, for example, a random access memory, read only memory, etc. While illustrated in this example as being separate from processing unit 520, it should be understood that all or part of primary memory 524 may be provided within or otherwise co-located/coupled with processing unit 520.

According to an embodiment, one or more portions of memory 522 may store signals representative of data and/or information as expressed by a particular state of memory 522. For example, an electronic signal representative of data and/or information may be “stored” in a portion of memory 522 by affecting or changing the state of such portions of memory 522 to represent data and/or information as binary information (e.g., ones and zeros). As such, in a particular implementation, such a change of state of the portion of memory to store a signal representative of data and/or information constitutes a transformation of memory 522 to a different state or thing.

Secondary memory 526 may include, for example, the same or similar type of memory as primary memory and/or one or more data storage devices or systems, such as, for example, a disk drive, an optical disc drive, a tape drive, a solid state memory drive, etc. In certain implementations, secondary memory 526 may be operatively receptive of, or otherwise configurable to couple to, a computer-readable medium 528. Computer-readable medium 528 may include, for example, any medium that can carry and/or make accessible data, code and/or instructions for one or more of the devices in system 500.

Computing device 504 may include, for example, an input/output 532. Input/output 532 is representative of one or more devices or features that may be configurable to accept or otherwise introduce human and/or machine inputs, and/or one or more devices or features that may be configurable to deliver or otherwise provide for human and/or machine outputs. By way of example but not limitation, input/output device 532 may include an operatively configured display, speaker, keyboard, mouse, trackball, touch screen, data port, etc.

While there has been illustrated and described what are presently considered to be example embodiments, it will be understood by those skilled in the art that various other modifications may be made, and equivalents may be substituted, without departing from claimed subject matter. Additionally, many modifications may be made to adapt a particular situation to the teachings of claimed subject matter without departing from the central concept described herein. Therefore, it is intended that claimed subject matter not be limited to the particular embodiments disclosed, but that such claimed subject matter may also include all embodiments falling within the scope of the appended claims, and equivalents thereof. 

What is claimed is:
 1. A system comprising: a dual inline memory module (DIMM) comprising one or more phase change memory (PCM) modules; a memory bus electronically connected to said system, wherein said PCM modules are electronically connected in parallel to said memory bus; and a basic input/output system (BIOS) configured to maintain parameters corresponding to said PCM modules, wherein the DIMM comprises a plurality of memory sites, at least some of the memory sites comprising PCM modules and at least some of the memory sites comprising DRAM modules, and wherein the DIMM is configured to cache write data corresponding to addresses corresponding to PCM modules in the DRAM modules.
 2. The system of claim 1, wherein said parameters include a value for additive latency of said PCM modules or a column address strobe (CAS) latency.
 3. The system of claim 1, wherein said PCM modules are associated with an additive latency that enables a column address to be provided to said DIMM immediately after a row address is provided to said DIMM.
 4. The system of claim 1, further comprising: dynamic random access memory (DRAM) cache memory to cache write data corresponding to particular addresses of said DIMM.
 5. The system of claim 1, wherein bank address bits correspond to multiple memory banks across multiple said one or more PCM modules.
 6. The system of claim 1, wherein said DIMM comprises a main memory of said system.
 7. The system of claim 1, wherein said one or more PCM modules comprise dynamic random access memory (DRAM) mode registers and/or a DRAM interface.
 8. A memory device comprising: a dual inline memory module (DIMM) adapted to electronically operate based, at least in part, on dynamic random access memory (DRAM) modules, wherein said DIMM comprises one or more phase change memory (PCM) modules and is configured to operate based on parameters maintained in a basic input/output system (BIOS), wherein the DRAM module is included in the DIMM, and wherein the DIMM is configured to cache write data corresponding to addresses corresponding to PCM modules in the DRAM modules.
 9. The memory device of claim 8, further comprising: a memory bus configured to electronically connect to a computing system, wherein said PCM modules are electronically coupled in parallel to said memory bus.
 10. The memory device of claim 8, further comprising: DRAM cache memory to cache write data corresponding to particular addresses of said DIMM. 